Hydrofoil impeller

Abstract

A hydrofoil impeller wherein the tip edge is straight and has a right angle with a radius extending from the central axis to the tip edge. In the central hub and in each of the blades the number of holes in each group of first and second holes is at least five. The pattern in which the holes are arranged in each of the respective groups of holes is elliptical having a center and a major axis which is substantially parallel to the radius and placed at a distance therefrom. The leading edge is, in the direction of rotation, behind an imaginary radial line intersecting the central axis of the shaft and the center of the ellipse, the leading edge being at an angle of 50°±2° in relation to the radial line. The area of the blade is divided into four planar portions by three straight bends.

The invention claimed is: 
     
       1. A hydrofoil impeller for producing fluid flow in an axial direction relative to a shaft rotating around its central axis in an agitated tank, said impeller comprising:
 a central hub which is connected to the shaft, the shaft defining an upper portion and an opposite, lower portion, the central hub being in the form of a flat plate with a uniform thickness and being perpendicular to the central axis, the central hub having three equally spaced groups of first bolt holes, wherein each group of first bolt holes is arranged to form a pattern, 
 three equally-spaced blades extending radially outwardly from the central hub, each blade having a root portion, said blade being in a form of a flat plate with a uniform thickness, said root portion of each blade having a corresponding group of second bolt holes arranged in a pattern corresponding to the pattern of a respective group of first bolt holes so that each group of second bolt holes can be aligned with the respective group of first bolt holes and bolts can be placed through the respective first and second bolt holes to form bolted joints, an each blade comprising a straight leading edge, a trailing edge and a tip edge, wherein:
 the tip edge is straight and has a right angle with a radius extending from the central axis to the tip edge, 
 the number of holes in each group of first and second bolt holes is at least five, 
 the pattern in which the first bolt holes and second bolt holes are arranged in each of the respective groups of first and second bolt holes is in a form of an ellipse having a center and a major axis which is substantially parallel to the radius and placed at a distance therefrom, 
 the leading edge is, in the direction to rotation, behind an imaginary radial line intersecting the central axis of the shaft and the center of the ellipse, said leading edge being at an angle of 50°±2° in relation to the radial line, 
 the trailing edge has two straight edge portions which are at an angle (β) of 150°±5° to each other, a tip of said angle (β) being located at a middle portion of the length of the trailing edge, said tip being rounded, 
 each blade defines an area that is divided into four planar portions by three straight bends which include:
 a first bend extending along the blade in a direction which is at an angle (γ) of 16°±2° in relation to the radius and, in the direction of rotation, forwards of the radius, said first bend dividing the blade to said root portion and a first profile portion, the root portion and the first profile portion meeting at the first bend such that the first profile portion is angled at an angle of 16°±2° towards the lower portion of the shaft from the root portion, 
 a second bend extending along the blade in a direction which is at an angle (σ) of 12°±2° in relation to the radius and, in the direction of rotation, backwards from the radius, said second bend dividing the blade further to a second profile portion, the first profile portion and the second profile portion meeting at the second bend such that the second profile portion is angled at an angle of 10°±2° towards the lower portion of the shaft from the first profile portion, and 
 a third bend extending along the blade in a direction which is at an angle (θ) of 21°±2° in relation to the radius and, in the direction of rotation, backwards from the radius, said third bend dividing the blade further to a third profile portion, the second profile portion and the third profile portion meeting at the third bend such that the third profile portion is angled at an angle of 8°±1° towards the lower portion of the shaft from the second profile portion. 
 
 
 
     
     
       2. The hydrofoil impeller according to  claim 1 , wherein the central hub is in the form of a triangular plate with rounded corners, each corner having one group of first bolt holes. 
     
     
       3. The hydrofoil impeller according to  claim 1 , wherein the length of the blade is 0.85×R±0.1×R, wherein R is the length of the radius from the central axis to the tip edge. 
     
     
       4. The hydrofoil impeller according to  claim 1 , wherein the corner between the leading edge and the tip edge is rounded with a radius of 0.125×R±0.02R, wherein R is the length of the radius from the central axis to the tip edge. 
     
     
       5. The hydrofoil impeller according to  claim 1 , wherein the corner between the trailing edge and the tip edge is rounded with a radius of 0.125×R±0.02×R, wherein R is the length of the radius from the central axis to the tip edge. 
     
     
       6. The hydrofoil impeller according to  claim 1 , wherein the thickness of the blade is 0.02×R±0.01R, wherein R is the length of the radius from the central axis to the tip edge.